1. Field of the Invention
The invention relates to a lamp unit in which a high pressure mercury lamp is located, and a process for light control thereof. The invention relates especially to a lamp unit for a projector which is used as a light source of a liquid crystal projector, a DLP (digital light processor) or the like, and a process for light control thereof.
2. Description of Related Art
In a projector device of the projection type, there is a need for illumination of images onto a rectangular screen in a uniform manner and with sufficient color reproduction. The light source is therefore a metal halide lamp which is filled with mercury and a metal halide. Furthermore, smaller and smaller metal halide lamps have been used recently, and more and more often point light sources are being produced, and lamps with extremely small distances between the electrodes are being used in practice.
Against this background, lamps with an unprecedentedly high mercury vapor pressure, for example, with pressures of 200 bar (roughly 197 atm) or more have been recently proposed instead of metal halide lamps. Here, due to the increased mercury vapor pressure, broadening of the arc is suppressed (the arc is contracted) and an extensive increase of the light intensity is desired; this is disclosed, for example, in U.S. Pat. No. 5,109,181 and in U.S. Pat. No. 5,497,049.
A lamp unit which is to be used for a projector comprises the above described mercury lamp, a concave reflector which surrounds it, and a front glass for the concave reflector. The arrangement of the front glass imparts a hermetically enclosing arrangement to the interior of the concave reflector. Alternatively, the interior of the concave reflector acquires an essentially hermetically enclosing arrangement, even if part is provided with a cooling opening. This hermetically enclosing arrangement in the above described lamp, which has been filled with a large amount of mercury, makes it possible for mercury to vaporize enough by, during lamp operation, the temperature being increased without being cooled by outside air. Thus, it no longer becomes necessary to have a special preheating device or the like which is used for complete vaporization of the mercury. Furthermore, it is possible to eliminate the defect that glass fragments and the like will spray out from the unit when, in the worst case, the lamp is damaged or the like.
On the other hand, in a projector device, there is the need for a light control function to control the screen illuminance according to the environment and the image projection situation. To meet this need, the light emitted from the lamp unit can be subjected to light control using a radiation attenuation means. With consideration of the need to reduce the size of the projector device, however, control of the intensity of the radiant light from the lamp unit, in and of itself, is required as a process for the above described light control in the inherent sense. Here, for example, in a bright room or for a large screen, by increasing the starting power for the lamp, its radiation intensity is increased while, in a relatively dark room or for a small screen, the starting power for the lamp is reduced.
However, since the above described lamp unit is built with a hermetically enclosing arrangement, with consideration of the nominal wattage of the lamp in steady-state luminous operation and of the inside volume of the interior of the unit in the vicinity, the range in which the starting power for the lamp can be changed is extremely narrowly restricted. Specifically, if the starting power for the lamp is unduly reduced to reduce the radiation intensity, a phenomenon is caused which is called xe2x80x9cnonvaporization of the mercury in the lampxe2x80x9d. This engenders the problem that the desired emission spectrum characteristic is not obtained. On the other hand, the temperature within the unit is extremely high when the starting power for the lamp is unduly increased to increase the radiation intensity. This can engender the problems that the electrodes and the like in the lamp are used up, that the film which has been deposited on the inside of the concave reflector is degenerated and that the lamp is damaged (broken).
The above described prior art is summarized below.
First, with respect to the light source of a projector device the following is desired:
With respect to the characteristic, a mercury lamp filled with a large amount of mercury, for example, a lamp with at least 0.15 mg/mm3, is desired. In a lamp unit using this lamp, with consideration of the reduction in size and the safety of the projector device, a hermetically enclosing arrangement or an arrangement which is only partly provided with cooling openings is desired.
Second, for a projector device, there is a great demand for a light control function as a lamp unit to adequately satisfy the many application purposes of the user of this device.
The invention was devised to yield a lamp unit for a projector which can adequately meet the aforementioned requirements.
A primary object of the present invention is to devise a lamp unit with a light control function for the light emitted from this lamp unit, for which a high pressure mercury lamp is used which is filled with at least 0.15 mg/mm3 mercury and which lamp unit has a hermetically enclosing arrangement, an essentially hermetically enclosing arrangement or an arrangement in which a flow path for actively flowing cooling air is formed.
The above object is achieved, in its widest aspect, for a lamp unit in which it comprises:
a high pressure mercury lamp of the short arc type with a wall load of at least 1 W/mm2 which is filled with at least 0.15 mg/mm3 mercury;
a concave reflector which surrounds this mercury lamp; and
a front cover which covers the front opening of this concave reflector,
a cooling means which can be controlled with respect to its cooling intensity for cooling of the concave reflector and/or the mercury lamp and
a means by which the radiant power of the mercury lamp can be changed, the cooling means and the means for controlling the lamp power being made such that, by controlling the two, a value in the range of 1 less than (Wxc3x97G/V) can be set, V (in cm3) being the inside volume of the concave reflector, W (in W) being the rated power of the mercury lamp and G (in W/mm2) being the wall load.
The suggested approach can be used both for hermetically enclosing and essentially hermetically enclosing arrangements of lamp units or also for those lamp units which are cooled forcefully by controlled feed of cooling air. For these different types of lamp units preferred ranges (Wxc3x97G/V) were determined; this is to be explained in detail below.
The object was achieved in accordance with the invention in a lamp unit with a hermetically enclosing arrangement or an essentially hermetically enclosing arrangement which comprises:
a high pressure mercury lamp of the short arc type with a wall load of at least equal to 1 W/mm2 which is filled with at least 0.15 mg/mm3 mercury;
a concave reflector which surrounds this mercury lamp; and
a front cover (also called the front glass) which covers the front opening of this concave reflector,
in which, in the range 1 less than (Wxc3x97G/V) less than 2, in conjunction with the cooling intensity of a cooling means with an intensity which can be changed with respect to the above described concave reflector and/or the above described mercury lamp, there is a means which changes the power of the mercury lamp, and thus, light control of the above described mercury lamp is enabled, where V (cm3) is the inside volume of the concave reflector, W is the rated power of the mercury lamp and G is the wall load.
Furthermore, in accordance with the invention, a process for light control of such a lamp unit is given.
The object is furthermore achieved in accordance with the invention in that the above described lamp unit has neither a hermetically enclosing arrangement nor an essentially hermetically enclosing arrangement, but an arrangement in which a flow path for active flow of the cooling air is formed in the interior and that the above described mercury lamp in the range of 1 less than (Wxc3x97G/V) can be subjected to light control, V (cm3) is the inside volume of the concave reflector, W is the rated power of the mercury lamp and G is the wall load.
As was described above, according to the invention, the concave reflector and the mercury lamp are cooled by means of a cooling means with an intensity which can be changed, and moreover, the cooling intensity thereof is carried out together with the light control of the mercury lamp. In this light control, it is specifically a matter of the fact that the power of the lamp can be changed. It was thus found that, for a small lamp unit which is used for a projector, both the above described cooling and also light control can be advantageously performed when numerical values which are derived in such a way that the inside volume of the concave reflector, the power of the mercury lamp and the wall load of the mercury lamp are taken into account and are considered to be factors which lie within a given range. There is no clear reason for the inside volume of the concave reflector, the power of the mercury lamp and the wall load of the mercury lamp to have been considered to be factors; however, it was found that the cause of the increase of temperature which is to be reduced by cooling depends on these factors.
Moreover, it was found that the above described numerical values in the following cases are in different ranges, specifically in the case in which the concave reflector is hermetically sealed, furthermore in the case in which the concave reflector has an essentially hermetically enclosing arrangement in which the concave reflector is provided partially with openings, and in the case in which in the concave reflector a flow path for the actively flowing cooling air is formed, i.e., the mercury lamp is located in a certain line for the cooling air.
The invention is described below in greater detail with reference to the accompanying drawings.